Field of the Invention
The invention relates to a method for the surface cleaning of small quartz-crystal pieces by subjecting them to the action of aqueous hydrofluoric acid, and to an apparatus for carrying out said method.
Quartz-crystal pieces which are used in the manufacture of vitreous shaped bodies are frequently contaminated on their surface with silicate impurities. The latter will dissolve in aqueous hydrofluoric acid much more rapidly than pure quartz. When quartz-crystal pieces so contaminated are retained in aqueous hydrofluoric acid for a sufficient length of time, the mineral impurities will therefore be completely dissolved while only a surface layer of minimal thickness will be removed from the quartz-crystal pieces. This discovery is utilized in industry in the surface cleaning of quartz-crystal pieces.
From German patent application DOS No. 24 31 928 there is known a method for the removal of various impurities, and particularly iron compounds, from quartz sand. In this method, the quartz sand and aqueous hydrofluoric acid are mixed at elevated temperature in a reactor, and acid and sand are then separated from each other by the use of a filter. In this method, the impure sand is acted upon by fresh, pure aqueous hydrofluoric acid, which, however, is consumed during cleaning by the formation of complex compounds, in particular fluosilicic acid. Since the hydrofluoric acid concentration is being reduced continually, there is no assurance with this method that mineral impurities of larger size are completely removed from quartz-crystal pieces.
It is an object of the present invention, therefore, to provide a reliable method for removal of mineral impurities adhering to the surfaces of quartz-crystal pieces, regardless of their size.